The rpincipal objectives of the Virus Research Unit during the period 1958-1972, when its investigative activities were supported by PHS Grant !I-01992, remain essentially unchanged. They are to carry out (1) Study of mammalian viral infectivity and cytopathogenicity, especially as these phenomena may be analyzed in vitro; (2) Studies on the relationship of viruses to oncogenic transformation; and (3) Clinico-virological studies undertaken with the purpose of (a) Extending knowledge of the clinical and epidermiological aspects of diseases caused by recognized viruses, (b) Improving or developing laboratory diagnostic techniques, (c) Revealing unknown viral agents, and (d) Developing specific prophylactic and therapeutic measures. Present major endeavors which we plan to continue are (1) Exploration of the use of virus-cell fusion techniques for the adaptation of certain viruses, particularly the agents of infectious and serum hepatitis, to growth in resistant cells, and for the detection of latent viruses; (2) Studies on cellular factors associated with resistance and susceptibility to virus infection, and on the mechanism of action of interferon; (3) Studies on virus-cell interactions in cells transformed by certain DNA and RNA rumor viruses; (4) Clinico-virological studies on individual cases and outbreaks of viral or suspected viral infections; and (5) Cooperative treatment studies of (a) Herpes simplex virus encephalitis, (b) Disseminated neonatal herpes simples virus infection, (c) Disseminated varicella-zoster virus infections in immunosuppressed patients, and (d) Recurrent cutaneous herpes simplex virus infections. These have been undertaken in order to evaluate the efficacy of inhibitors of DNA synthesis (or neutral red and light) as chemotherapeutic agents, to further define the natural history of these diseases, and to develop more rapid and reliable means of specific diagnosis.